Change `ReadModel` and `Factory`, use new `TypeConverter` interface

This updates `ReadModel` and `Factory` to use the new interface
for `TypeConverter`. This involved calling the type methods
directly instead of going through `convert`. This also allowed
removing the `convert` method.
Merge pull request #179 from redding/jcr-rm-fac-update-for-type-converter

Change `ReadModel` and `Factory`, use new `TypeConverter` interface